Whatever it was that set them off, the birds were making so much noise that they attracted Portia down from the rafters of the garage, where she had been exploring the recent changes resulting from my cleaning spree (all the fascinating maze of boxes, gone!) and sent her out to nose around in the bushes where some of the birds had taken refuge at her approach. She didn't catch any of them, and the hummingbirds buzzed off to complete their business in some less busy place. After that the day was rather dull, except for the paramedics and a fire engine visiting a house up the block. No copulating birds were involved in that event, so I didn't pay much attention to it.
There probably won't be any such displays tomorrow, as the cold is returning and snow is once again a possibility. In fact another wintry week is likely. There could be more snow falling within a few hours. I'm glad I got the garage semi-cleaned when I did. Tomorrow I'll be huddling in the house under a pile of blankets. I feel sorry for those poor hummingbirds, though. Such a short honeymoon they'll have had.